This application relates generally to inspecting objects, and more specifically to methods and apparatus for inspecting objects using a light measurement system.
Objects are sometimes inspected, for example, to determine a size and/or shape of all or a portion of the object and/or to detect defects in the object. For example, some gas turbine engine components, such as turbine or compressor blades, are inspected to detect fatigue cracks that may be caused by vibratory, mechanical, and/or thermal stresses induced to the engine. Moreover, and for example, some gas turbine engine blades are inspected for deformations such as platform orientation, contour cross-section, bow and twist along a stacking axis, thickness, and/or chord length at given cross-sections. Over time, continued operation of the object with one or more defects may reduce performance of the object and/or lead to object failures, for example, as cracks propagate through the object. Accordingly, detecting defects of the object as early as possible may facilitate increasing the performance of the object and/or reducing object failures.
To facilitate inspecting objects, at least some objects are inspected using a light measurement system that projects a structured light pattern onto a surface of the object. The light measurement system images the structured light pattern reflected from the surface of the object and then analyzes the deformation of the reflected light pattern to calculate the surface features of the object. More specifically, during operation, the object to be inspected is typically coupled to a test fixture and positioned proximate to the light measurement system. A light source is then activated such that emitted light illuminates the object to be inspected. However, a resultant image of the object may include noise caused by multiple bounce reflections of the emitted light. Such noise may result in reduced image quality and poor measurement results, possibly leading to an incorrect interpretation of surface features of the object. For example, light reflected off of prismatic surfaces of the object may cause multiple bounce reflections. Moreover, and for example, multiple bounce reflections may be caused by inter-reflections between the object and portions of the test fixture illuminated by the light source. For example, multiple bounce reflections may be caused if the test fixture has a shape or finish that casts reflections on the object, and/or if the object has a relatively mirror-like finish that reflects an image of the test fixture.
Some light measurement systems use a pair of crossed polarized filters to reduce, eliminate, and/or identify noise caused by multiple bounce reflections. However, crossed polarized filters may require multiple images to be taken of the object to reduce or eliminate multiple bounce reflections because reducing or eliminating such reflections may require different orientations of the filters. Moreover, multiple images may also be required to analyze slope, texture, material, and/or other features of the object because analyzing differently angled reflections may require different orientations of the filters.